Rheumatoid arthritis (RA) is the most common systemic autoimmune disease in the United States, affecting 1-2% of the adult population. Although joints and synovium are the primary targets in this disorder, extra-articular manifestations involving the eyes, skin, heart, vasculature, and lungs can lead to significant morbidity as well as excess mortality. Among the various pulmonary complications that occur in RA, interstitial lung disease (ILD) is the most damaging, with effects that range from subclinical inflammation/scarring to end stage pulmonary fibrosis. Because earlier, subclinical forms of rheumatoid arthritis-associated interstitial lung disease (RA-ILD) may represent more treatable precursors of pulmonary fibrosis, non-invasive peripheral biomarkers are needed to identify this pulmonary complication in advance of clinical decompensation. Based on the hypothesis that CXCR3-binding chemokines and various matrix metalloproteinases play a significant role in driving inflammation as well as tissue damage in RA-ILD, Specific Aim 1 employs multiplex ELISA in RA patients with/without various forms of ILD to correlate the peripheral blood/serum levels of these signaling molecules and degradative enzymes with stage of lung disease. Extending the analysis of Specific Aim 1, Specific Aim 2 defines composite biomarker profiles of serum protein expression patterns in a parallel cohort of VA-derived RA patients with varying stages of ILD, validating the use of serum multiplex ELISA and elucidating the contribution of important secondary factors such as smoking. Finally, Specific Aim 3 complements this molecular phenotyping approach, utilizing immunoprecipitation and ELISA-based techniques to delineate serum anti-citrullinated protein autoantibody profiles that correlate with the presence or absence of ILD. Through the development of peripheral blood biomarker signatures associated with RA-ILD, these collective approaches will provide insight regarding the pathogenesis of RA-ILD and other forms of immunologically mediated lung disease. More importantly, defining the molecular phenotype of ILD will identify therapeutic targets facilitating early treatment intervention in this potentially devastating extra-articular complication of RA. PUBLIC HEALTH RELEVANCE: Rheumatoid arthritis (RA) is the most common systemic autoimmune disorder in the United States Veteran population, though the exact prevalence is unknown. Among the most significant and serious extra-articular complications of RA is interstitial lung disease (ILD). Because early, subclinical forms of RA-ILD may be precursors to pulmonary fibrosis, readily obtainable biomarkers are needed to facilitate early diagnosis and therapeutic intervention in this condition that is likely tied to highly prevalent environmental risk factors such as smoking. In short, this proposal involves the development of novel peripheral blood biomarkers that will not only serve as tools in the clinical assessment of RA-ILD, but will also lend insight regarding pathogenesis and the role of smoking in this potentially devastating process. By extension, these studies will advance our understanding of other forms of connective tissue disease-associated ILD as well as smoking-related disorders that include idiopathic pulmonary fibrosis.